The present invention relates generally to networks and, more particularly, to providing global positioning system (GPS) time and assistance data in a wireless communication network.
Today's mobile communications users desire increasingly fast, more robust and more efficient wireless communication systems. Accordingly, manufacturers and standards bodies are continually improving current systems and implementing new standards to support additional capabilities. One such standard for providing data over both Global System for Mobile communications (GSM) and Time Division Multiple Access (TDMA)/136 systems is the Enhanced General Packet Radio Service (EGPRS).
An EGPRS-136 system integrates the TIA/EIA-136 circuit-switched air interface with the General Packet Radio Service (GPRS) as specified in GSM. More specifically, EGPRS-136 supports circuit-switched services on a 30 kHz air-interface as specified in TIA/EIA-136 and TIA/EIA-41 (ANSI-41) and packet data service on a 200 kHz air interface as specified in GSM. Thus, an EGPRS-136 mobile terminal may send and receive voice calls, as well as, send and receive e-mails, surf the web, etc.
One area of wireless communications that has seen a lot of attention in recent years is the area of mobile terminal positioning. System Assisted Mobile Positioning through Satellite (SAMPS) is a positioning solution for TDMA/ANSI-41 that utilizes the existing GPS infrastructure. A SAMPS-capable mobile terminal is equipped with a GPS receiver to support the positioning procedures. The SAMPS service also utilizes the data capabilities of TIA/EIA-136 networks to enhance the performance of GPS-equipped mobile terminals by providing “assistance.”
For example, a SAMPS-capable mobile terminal may be provided with the following pieces of assistance data by the SAMPS service: Almanac, Ephemeris and Clock Corrections, Ionospheric Corrections, Reference Time, and Reference Location information. The Almanac provides a long term model for the orbital parameters of the satellites and is useful in determining a coarse position of the satellites at a given reference location at a certain reference time.
The Ephemeris and Clock Corrections allow accurate computation of the positions of the GPS satellites at the time of the measurements. Mobile terminals may use the Ionospheric Corrections to compensate for ionospheric delays through the atmosphere.
Reference Location provides a typically crude estimate, to within approximately 50–100 km (in some cases it may be more accurate), of the mobile terminal's current position. Reference Location may be obtained either from the network (e.g., from control channels) or from previous recent position fixes using the GPS receiver.
Reference Time provides an estimate of the current GPS time. Reference Time may be obtained, for example, from a digital control channel (DCCH) by sending a relationship between the GPS time and time on the DCCH for some epoch of the GPS time. When the mobile terminal is camping on the DCCH, the DCCH time is available at any instance. The mobile terminal may compute the GPS time at a given instance by adding the difference between the current epoch and the epoch for which the GPS time to DCCH time relationship was provided to the GPS time.